DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



361 



curves referred to are nearly obliterated (vide rs, tu). At fig. 34 the wing is 

 shown at the end of the down stroke, and the curves are reversed, as a com- 

 parison of c d, ef of fig. 32 with g h, ij of fig. 34 will satisfactorily prove. 



In the dragon-fly similar figure of 8 curves are developed along the anterior 

 and posterior margins of the wings at the beginning, middle, and termination of 

 the down stroke, as an examination of figs. 35, 36, 37, and 38 will show. If 



Fig. 35. 



Fig. 36. 



Fig. 37- 



Fig. 38. 



the letters c d, ef of fig. 35 (dragon-fly) be compared with corresponding letters 

 of fig. 32 (butterfly) ; the letters r s, t u of fig. 37 (dragon-fly) with similar letters 

 of fig. 33 (butterfly), and the letters gh, ij of fig. 36 (dragon-fly) with the same 

 letters of fig. 34 (butterfly), it will at once be perceived that the curves which 

 these letters represent are identical in both cases. At fig. 38 the wings are 

 represented as seen at the beginning and end of the down stroke, the arrows r, s 

 giving the range or play of the wings. The letters df of this figure (anterior 

 wing at beginning of down stroke) correspond with df of fig. 35 ; the letters g h 

 ij (anterior wing at end of down stroke) corresponding with similar letters in fig. 

 36. Fig. 38 shows how the posterior margin of the wing (/) is screwed dowmvards 

 and forwards (j) during the down stroke (compare with a, b, c of figs. 16 and 

 17, page 349, and read remarks on the dragon-fly's wing at pages 335 and 350).'"" 



* The wing area in insects is usually greatly in excess of what is absolutely required for flight, as 

 the following experiments made, with the common white and brown butterfly and dragon-fly will show : — 



1. Removed posterior halves of first pair of wings of white butterfly. Flight perfect. 



2. Removed posterior halves of first and second pairs of wings. Flight not strong but still per- 

 fect. If additional portions of the posterior wings were removed, the insect could still fly, but with 

 great effort, and came to the ground at no great distance. 



3. When the tips (outer sixth) of the first and second pairs of wings were cut away, flight was in 

 no wise impaired. When more was detached the insect could not fly. 



